Title of Presentation: GaN-based Robust Micro Pressure and Temperature Sensors for Extreme Planetary Environments
Primary (Corresponding) Author: Kyung-ah Son
Organization of Primary Author:
Co-Authors: B. Yang, A. Liao, I. P. Steinke, Y. Liu, P. P. Ruden, X. Ni, J. Xie, N. Biyikli, H. Morkoç, R. E. Young, and A. Colaprete
Abstract: We are developing robust GaN-based microsensors that are capable of simultaneous temperature and pressure measurements in extreme planetary atmosphere. Due to the large band gaps (3.4-6.1 eV) and strong atomic bonds, GaN and AlGaN compound semiconductors have favorable mechanical properties and thermal and chemical stabilities along with minimal problems arising from the unwanted optical or thermal generation of charge carriers. Therefore they are ideal materials for sensors for extreme and harsh environments. One of the unique advantages of GaN-based devices is that AlGaN/GaN heterostructures develop sheet charges at the hetero-interfaces due to the piezoelectric and spontaneous polarizations between AlGaN and GaN layers. Applied stress modulates this interfacial polarization charge due to differences in the piezoelectric coefficients of AlGaN and GaN, and therefore the barrier height is modulated. We utilize this stress-induced modulation of the barrier height for pressure sensing. Mobility of the electrons in the polarization sheet changes with temperature due to scattering. We use this temperature-induced mobility change for temperature measurements.
Among the various AlGaN/GaN heterostructure devices, we have investigated n-GaN/AlxGa1-xN/n-GaN (n-I-n) vertical transport devices and high electron mobility transistors (HEMTs) for pressure and temperature sensing applications. Our research performed for n-I-n sensors fabricated with various compositions (x = 0.1, 0.15, & 0.3) of AlxGa1-xN suggests that electrical currents decrease linearly and reversibly with increased pressure within the range that we measured (0-6 kbar), and this effect becomes more significant with higher AlN compositions in the AlxGa1-xN layer.
The current-voltage characteristics of various Al0.3Ga0.7N/n-GaN HEMT sensors have been measured under hydrostatic pressure of 0-2 kbar. The results show that the drain current increases with pressure and the maximum relative increase occurs when the gate bias is near threshold and drain bias is slightly larger than saturation bias. The increase of the drain current is associated with a pressure-induced shift of the threshold voltage. The linearity and reversibility in pressure response observed with both n-I-n and HEMT sensors suggest that they are promising for pressure sensor applications in extreme environments. Temperature effects on electrical properties of the GaN-based sensors have also been measured, and detailed analysis on the results is in progress.